The invention is generally related to the installation of pipeline offshore and more particularly to the reel structures used in such installations.
The installation of submarine pipelines by reeling of steel pipe on to a reel, transporting the loaded reel to the pipeline installation site and un-reeling the pipe from a marine vessel offshore is a well established art. The cost advantages of reeled pipeline installation compared to other means of submarine pipeline installation include reduced amount of labor required to work offshore, a reduced amount of marine equipment and vessels required to support the installation operations, and faster pipeline installation speeds which reduce the exposure of the installation to offshore weather delays.
Key to the reeled pipeline installation method is the process of joining by welding up normally manufactured lengths of steel pipe joints into a continuous string of pipe which can then be reeled (“spooled”) up on to the pipe reel. Because of the strains in the steel pipe due to reeling, the weld quality must be superior to pipe welds typically used for non-reeled pipeline installations. This requires a large onshore facility (to store long strings of pipe) and a highly skilled work force. Such a facility is known as a “pipe spooling base”. Longer strings are preferred because this reduces the number of times the reeling on process must be stopped to allow another string of pipe to be welded on.
Unless the pipe reel is small enough that it can practically be shipped and loaded onto the vessel, the reeled pipe lay vessel must transit to/from the pipe spooling base so as to allow the pipe to be reeled up onto a reel installed on the vessel.
Once at the pipe spooling base, the pipe lay vessel must then stand by as the initial pipe string is engaged on the reel, reeled up, the subsequent string welded on to the end of the string previously reeled on to the reel, and the repeat of the welding and reeling on process until such time as the reel is fully loaded with strings of pipe. Once loaded, the pipe lay vessel must then transit to the pipeline installation site.
In order to expediently reel up pipe on the pipe lay vessel the pipe spooling base facility must provide long stalks of pipe, thereby minimizing the amount of time spent welding on strings of pipe.
The need for the reeled pipe lay vessel to transit to a distant pipe spool base, the high fixed cost of establishing such a facility with a long pipe string storage capacity and the need for the vessel to stand by during the reeling up of the pipe are the primary economic cost drivers of reeled pipe lay installation for larger reeled pipelines. In order to decrease the amount of reeled pipe lay vessel travel cost to/from the pipe spool base, additional fixed operating cost must be incurred to build more pipe spooling bases closer to the pipeline installation sites.
For smaller sized pipe (including coiled steel tubing which can be used in pipeline service) smaller reels can be loaded with pipe onshore at a central reeling facility and the smaller reels lifted and transported to a suitable location where they can be situated on a suitable pipe lay vessel.
In such cases where small reels are used, under-roller machines used to support and rotate the reel from the rim of the reel or a machine used to engage the reel axis on a reel stand are used. The machines used to handle small reels of pipe can be mounted on any suitably sized vessel of opportunity to allow that vessel to work as a reeled pipe lay vessel. The reel handling machines used with such small reels are typical of machines used to dispense coiled tubing during oil well down-hole tubing operations and the laying of flexible pipelines. The foregoing allows smaller pipelines to be reeled at locations remote (such as a single central location) from where the installation vessel may eventually be loaded with the small reels. This removes the economic disadvantage of needing to take the installation vessel to the point where the pipe is reeled up or establishing and operating multiple spool bases.
For larger pipelines installed by the reeled pipe lay method, large reels are typically installed permanently to vessels dedicated to reeled pipe lay installations. The installation of the reels on these vessels is essentially permanent because the reel support structure must be very robust to tolerate the dynamic loads acting on the reel due to movements of the vessel in the seaway. These dedicated vessels must transit to and from distant reeling bases in order to reel up pipe, or costly reeling facilities must be established to otherwise minimize the transit distance sailed by the reeled pipe lay vessel.
The large reels must be installed on the reeled pipe lay vessel using substantial bearings and drive systems to insure robust mechanical performance of the system during reeling operations. These systems must precisely engage the reel to perform reliably. When lifting large loaded reels of pipe onto the vessel these systems are at risk of damage due to incidental contact and impact loads. Large reels loaded with pipe typically weigh 2,500 tons. The present invention is directed to a reel capable of a loaded 3,000 ton weight. Impact damage to the bearings and drive systems will result in mechanical problems and aborted reeling operations corresponding to a great financial risk.
Because of the technical challenges related to lifting and landing large loaded reels on to a reeled pipe lay vessel there has been little practical use of large lifted reels for reeled pipeline installations.
As such, all of the dedicated reeled pipe lay vessels currently in service have reels which are permanently installed on the vessel and the vessel must load pipe by reeling up pipe from a reeling facility and the operators of these dedicated reeled pipe lay vessels have established a multitude of pipe spooling bases around the world to support the vessels and reduce vessel travel cost/time. Another disadvantage of vessels dedicated to laying of large pipe is that the large drums required for large rigid pipe limits the versatility of these vessels by limiting the capacity of flexible pipe or tubing that may be placed on reels with the larger drums even though the flexible pipe or tubing has greater bending capability than steel pipe and does not require the larger drum.
From the above, it is readily understood that there is a need for the ability to supply reeled pipe onto a reel lay vessel that is more time and cost efficient than having the vessel make multiple trips to pipe welding and spooling base and/or having multiple, expensive pipe spooling bases around the world.